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I2O                         RELATIONSHIP OF CETACEA                        CHAP.
of this group. A short re"simi(5 of what is at present thought
of the systematic position of this anomalous order is appro-
priate here. Albrecht went so far as to regard the Cetacea as
the. nearest group of animals to the hypothetical Proinamniaiia.1
But discounting his arguments by the removal of such of them
as relate to structure plainly altered by the singular mode of
life of these creatures, there is really a great deal to be said in
favour of his view.
The chief facts which argue a primitive position among
mammals for the Cetacea are perhaps : (1) the slight union of
the rami of the lower jaw; (2) the occasionally rather marked
traces of the double constitution of the sternum; (3) the long
and simple lungs ; (4) the retention of the testes within the
body-cavity; (5) the occasional presence (in JBalaenoptera) of a
separate supra-angular bone. These points, however, are but few,
and are not of such great weight as those which ought to be pre-
sent to establish a claim to separate treatment for the Cetacea
as opposed to the Eutheria. If this group of mammals can be
tacked on anywhere, it appears to us that the nearest relatives
are not, as is sometimes put forward, the IJngulata or the
Carnivora, but the Edentata. There are quite a number of
rather striking features in which a likeness is shown between
these apparently diverse orders of mammals. The chief ones
are these: (I) the existence of traces of a hard exoskeleton, of
which vestiges remain in the Porpoise; (2) the double articula-
tion of the rib of the Balaenopterids to the sternum, with which
compare the conditions obtaining in the Great Anteater; (3) the
concrescence of some of the cervical vertebrae ; (4) the share
which the pterygoids may take in the formation of the hard
palate; (5) the fact that in the Porpoise, at any rate,as in many
Edentates, the vena eava, instead of increasing in size as it
approaches the liver, diminishes.
Another group which is perfectly isolated is that of the
Sirenia. The alliance advocated by some with the Cetacea, and-
quite recently renewed by Professor Haeckel,is contradicted by so
many important features that it seems necessary to abandon it.
The recent discovery of a fossil Sirenian jaw by Dr. Lydekker with
teeth highly suggestive of those of Artiodactyla, may prove a clue.
A third group which is BO isolated as to have been, placed in a
1 Anat. An*, i. 1886, p, 338 ; and see Weber, ibid, ii, 1887, p. 42.